Evaluation method for the intensity of popcorn aroma in rice

Abstract

The invention discloses a method for evaluating the aroma intensity of popcorn fragrance in rice: firstly, the rice is steamed to prepare cooked rice, then solid phase microextraction is used to enrich volatile compounds, and then GC-MS analysis is performed, and the relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran are obtained by data analysis, and then the aroma quality score is obtained by calculation according to the contents of the three. The method of the invention can replace the traditional sensory evaluation method to evaluate the aroma intensity of popcorn fragrance in rice.

Description

Technical Field

[0001] The invention relates to the technical field of food detection, and in particular to a method for evaluating the aroma intensity of popcorn aroma in rice. Background Art

[0002] With the development of social economy and the improvement of people's living standards, people have higher and higher requirements for rice quality. The smell quality of rice is one of the important criteria for consumers to choose rice. Consumers prefer fragrant rice with special fragrance and pleasant aroma. The evaluation methods of rice smell quality are mainly divided into sensory evaluation method and instrumental method. The sensory evaluation method is mainly evaluated by chewing raw rice, smelling raw rice or rice tissue after heating or soaking in potassium hydroxide, or tasting steamed rice. The comprehensive sensory results are obtained. They are mostly used to distinguish fragrant rice from non-fragrant rice, score fragrance, etc., but they have the disadvantages of strong subjectivity, poor repeatability, and laboriousness. The instrumental method has shown great application potential in the qualitative and quantitative analysis of volatile compounds and the distinction between different rices, but it is insufficient in the quantitative evaluation of aroma intensity, mainly because the chemical basis of aroma quality is unclear and there is a lack of clear and effective aroma quality evaluation indicators. Therefore, the current method of rice aroma evaluation is still stagnant in relying on sensory methods that are laborious and subjective. Therefore, establishing an efficient, objective and repeatable rice aroma intensity evaluation method will greatly improve the efficiency of rice aroma quality evaluation, which will play an important role in promoting the development of high-quality rice industry and promoting the agricultural economy. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for evaluating the aroma intensity of popcorn aroma in rice.

[0004] In order to solve the above technical problems, the present invention provides a method for evaluating the aroma intensity of popcorn aroma in rice: first, the rice is steamed to prepare cooked rice, then solid phase microextraction is used to enrich the volatile compounds, followed by GC-MS analysis, and the relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran are obtained through data analysis, and then the aroma quality score is calculated according to the contents of the three.

[0005] As an improvement of the method for evaluating the aroma intensity of popcorn aroma in rice of the present invention, the method comprises the following steps:

[0006] 1) Sample preparation:

[0007] Steaming the rice to obtain cooked rice (according to conventional standards);

[0008] 2) Enrichment of volatile compounds:

[0009] While still hot, weigh (5±0.1) g of rice into a 30 mL extraction bottle, add 10 μL of 1 μg / mL 2-methyl-3-heptanone as an internal standard, and tighten the bottle cap; insert the extraction head into the bottle for extraction, perform solid phase microextraction in a water bath at 80±10℃ for 30±3 min, and then remove the extraction head;

[0010] 3) GC-MS analysis:

[0011] Insert the extraction head into the GC injection port for GC-MS analysis to obtain chromatographic mass spectrometric data of the sample (chromatographic mass spectrogram of the sample);

[0012] 4) Data analysis:

[0013] The contents of 2-acetylpyrroline, hexanal, 2-pentylfuran and total compounds were obtained by internal standard method, and the relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran in total compounds were further obtained;

[0014] 5) Aroma intensity evaluation:

[0015] The aroma intensity score of popcorn aroma was calculated based on the relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran.

[0016] As a further improvement of the method for evaluating the aroma intensity of popcorn aroma in rice of the present invention, in step 3):

[0017] Chromatographic conditions: Column temperature was programmed to maintain at 40°C for 5 min, then increased to 230°C at 5°C / min and maintained for 10 min; injection port temperature was 250°C; carrier gas: high-purity helium (purity>99.999%); flow rate was 1.0 ml / min; split ratio was 5:1;

[0018] Mass spectrometry conditions: electron impact (EI) ion source, ion source temperature of 230°C; ionization energy of 70 eV; full scan mode, scan range of m / z 40-500; quadrupole temperature of 150°C, connector temperature of 240°C.

[0019] Note: When the extraction head is at the injection port of the gas chromatograph, under high temperature conditions, the volatile compounds adsorbed in the extraction head are desorbed and enter the gas chromatography column for separation, and then enter the mass spectrometer for detection, thereby obtaining the gas chromatography mass spectrum of the volatile compounds in the sample to be tested. That is, the data directly obtained through this "GC-MS analysis" is the chromatographic mass spectrum of the volatile compounds;

[0020] To ensure accuracy, three replicates can be set for each sample, that is, 2)-3) can be repeated three times.

[0021] As a further improvement of the method for evaluating the aroma intensity of popcorn aroma in rice of the present invention, step 4) is:

[0022] The chromatographic mass spectrometry data obtained in step 3) above were imported into MassHunter software, and compounds were searched by chromatogram deconvolution or integral search, and compounds were identified using the NIST database, with a matching degree of 60% set; the content of the main compound in the sample was calculated based on the retrieved compound peak area and internal standard peak area (when N repetitions were set, the average value was taken); and 2-acetylpyrroline (x 1 )、hexanal(x 2 )、2-pentylfuran(x 3 )'s relative content.

[0023] As a further improvement of the method for evaluating the aroma intensity of popcorn aroma in rice of the present invention, step 5) is:

[0024] The relative content of hexanal and the relative content of 2-pentylfuran are both 9% as the cutoff point; if the relative content of hexanal and the relative content of 2-pentylfuran are both less than 9%, the aroma quality score is y = 0.6751x 1 +7.3553; otherwise, the aroma quality score is y=-0.05791x 2 -0.04181x 3 +8.4672.

[0025] It should be emphasized that: in the invention, it was found in the study that 2-acetylpyrroline presents an obvious popcorn aroma, and the higher the concentration, the stronger the popcorn aroma; while hexanal and 2-pentylfuran have certain grassy and aldehyde aromas, which are not liked by the evaluators when the concentration is too high, and have a certain masking effect on the popcorn aroma. When the ratio of hexanal and 2-pentylfuran in the sample exceeds a specific ratio, its sensory evaluation has no obvious correlation with 2-acetylpyrroline, but shows an obvious negative correlation with the ratio of hexanal and 2-pentylfuran. Therefore, the present invention is to obtain the above empirical formula through sample determination and sensory evaluation under the premise of a large number of experimental verifications. Thus, the content described in step 5) is obtained.

[0026] As a further improvement of the method for evaluating the aroma intensity of popcorn aroma in rice of the present invention:

[0027] The standard adopted in step 1) is the National Standard of the People's Republic of China GB / T 15682-2008.

[0028] The present invention is a method for evaluating the aroma intensity of popcorn in rice by using the relative content of volatile compounds:

[0029] The beneficial effects of the present invention are mainly reflected in:

[0030] 1. The method of the present invention can objectively and accurately evaluate the aroma intensity of popcorn aroma in rice.

[0031] 2. The method of the present invention can replace the traditional sensory evaluation method to evaluate the aroma intensity of popcorn aroma in rice. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0033] Example 1: A method for evaluating the aroma intensity of popcorn aroma in rice, using 19 rice samples as test samples, and each sample is subjected to the following steps in sequence:

[0034] 1) Sample preparation: Rice was steamed and cooked according to the standard (GB / T 15682-2008);

[0035] 2) Enrichment of volatile compounds:

[0036] Weigh about 5g of cooked rice while it is still hot and place it in a 30mL extraction bottle. Add 10uL of 1ug / mL 2-methyl-3-heptanone internal standard and tighten the bottle cap. Insert the extraction head above the rice in the extraction bottle for extraction. Perform solid phase microextraction in an 80℃ water bath for 30 minutes and then remove the extraction head.

[0037] 3) GC-MS analysis:

[0038] The extraction head was inserted into the injection port of the gas chromatograph in manual injection mode for GC-MS analysis.

[0039] Chromatographic conditions: Column temperature was programmed to maintain at 40°C for 5 min, then increased to 230°C at 5°C / min and maintained for 10 min; injection port temperature was 250°C; carrier gas: high-purity helium (purity>99.999%); flow rate was 1.0 ml / min; split ratio was 5:1.

[0040] Mass spectrometry conditions: electron impact (EI) ion source, ion source temperature of 230°C; ionization energy of 70 eV; full scan mode, scan range of m / z 40-500; quadrupole temperature of 150°C, connector temperature of 240°C.

[0041] When the extraction head is at the injection port of the gas chromatograph, under high temperature conditions, the volatile compounds adsorbed in the extraction head are desorbed and enter the gas chromatography column for separation, and then enter the mass spectrometer for detection, thereby obtaining a gas chromatography-mass spectrum of the volatile compounds in the sample to be tested. That is, the data directly obtained through this "GC-MS analysis" is the chromatographic mass spectrum of the volatile compounds.

[0042] Repeat the above steps 2) to 3) three times.

[0043] 4) Data analysis:

[0044] The chromatographic mass spectrometry data obtained in step 3) above were imported into MassHunter software, and the compounds were searched by chromatogram deconvolution. The compounds were identified using the NIST database, and the matching degree was set to 60%. The content of the main compound in the sample was calculated based on the retrieved compound peak area and internal standard peak area, and the average value of 3 times was taken. The content of 2-acetylpyrroline (x 1 )、hexanal(x 2 )、2-pentylfuran(x 3 The relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran in 19 samples and their relative contents to the total compounds are shown in Table 1.

[0045] Table 1. Relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran in 19 samples

[0046]

[0047]

[0048] Taking sample 1 as an example, the following specific instructions are given:

[0049] Step 3) The chromatographic mass spectrometry data of the volatile compounds of sample 1 obtained are imported into masshunter, and the compounds are searched by chromatogram deconvolution. The compounds are identified using the NIST database to obtain the peak areas of the main volatile compounds of sample 1. The peak areas of the retrieved compounds and the internal standard peak areas are used to calculate the contents of the main compounds in the sample. 2-乙酰基吡咯啉 =A 2-乙酰基吡咯啉 / A 内标 ×c 内标 =8432877 / 12949221×10uL×1ug / mL / 5g=1.30ng / g;

[0050] C 己醛 =A 己醛 / A 内标 ×c 内标 =246019805 / 12949221×10uL×1ug / mL / 5g=38.00ng / g;

[0051] C 2-戊基呋喃 =A 2-戊基呋喃 / A 内标 ×c 内标 =102461728 / 12949221×10uL×1ug / mL / 5g=15.83g / g;

[0052] C 总 =A 2-戊基呋喃 / A 内标 ×c 内标=965142527 / 12949221×10uL×1ug / mL / 5g=149.07g / g;

[0053] Repeat 3 times, c 2-乙酰基吡咯啉 The values ​​were 1.30ng / g, 1.98ng / g and 1.69ng / g respectively, with an average value of 1.66ng / g; C 2-戊基呋喃 The values ​​were 38.00 ng / g, 49.31 ng / g and 42.73 ng / g respectively, with an average value of 43.35 ng / g. 2-戊基呋喃 They were 15.83ng / g, 43.67ng / g and 31.45ng / g respectively, with an average of 30.31ng / g; C 总 They were 149.07ng / g, 229.58ng / g, and 177.02ng / g respectively, with an average of 185.24ng / g.

[0054] Then calculate 2-acetylpyrroline (x 1 )、hexanal(x 2 )、2-pentylfuran(x 3 ) relative content, x 1 =c 2-乙酰基吡咯啉 / c 总 =1.66 / 185.22=0.89%, x 2 =c 己醛 / c 总 =43.35 / 185.22=23.40%, x 3 =c 2-戊基呋喃 / c 总 =30.31 / 185.22=16.37%.

[0055] 5) Aroma intensity evaluation: The relative content of hexanal and 2-pentylfuran is 9% as the cutoff point. If the relative content of hexanal and 2-pentylfuran is less than 9%, the aroma intensity score is y = 0.6751x 1 +7.3553 (Formula 1); otherwise, the aroma intensity score is y = -0.05791x 2 -0.04181x 3 +8.4672 (Formula 2). The popcorn aroma intensity score was calculated based on the relative contents of 2-acetylpyrroline, hexanal, and 2-pentylfuran in the sample (Table 2).

[0056] Table 2. Popcorn aroma intensity scores obtained according to the method of the present invention in 19 samples

[0057]

[0058]

[0059] Verification test 1: Invite 5 rice aroma quality evaluation experts to score the popcorn aroma intensity of the 19 rice samples in Example 1 according to the rice aroma evaluation method in NY / T 596-2002 "Fragrant Rice". The specific scoring criteria are: very strong 9-10 points; strong 7-8 points; medium 5-6 points; weak 3-4 points; just recognized or threshold 1-2 points; no 0 point. The average value is taken as the final aroma intensity sensory score (Table 3).

[0060] Table 3. Popcorn aroma intensity scores of 19 samples obtained according to the agricultural industry standard method

[0061]

[0062]

[0063] The popcorn aroma intensity scores of 19 rice samples obtained by the method of the present invention are basically consistent with the measurement results obtained by the standard sensory evaluation method of the agricultural industry. Therefore, it is feasible to determine the popcorn aroma intensity in rice based on the relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran in rice.

[0064] In addition, the inventors also found in the process of invention that the cut-off point of 9% for the relative content of hexanal and 2-pentylfuran is a very important parameter. If this cut-off point is too high or too low, no matter what aroma quality scoring formula is used, the sample test conclusion will be significantly different from the conclusion of Table 3.

[0065] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for evaluating the aroma intensity of popcorn aroma in rice, characterized in that: First, the rice is steamed to prepare cooked rice, and then the volatile compounds are enriched by solid phase microextraction, followed by GC-MS analysis, and the relative contents of 2-acetylpyrroline, hexanal and 2-pentylfuran are obtained by data analysis, and then the aroma quality score is calculated according to the contents of the three; the method comprises the following steps: 1) Sample preparation: Steaming rice to obtain cooked rice; 2) Enrichment of volatile compounds: While still hot, weigh (5±0.1) g of rice into a 30 mL extraction bottle, add 10 μL of 1 μg / mL 2-methyl-3-heptanone as an internal standard, and tighten the bottle cap; insert the extraction head into the bottle for extraction, perform solid phase microextraction in a water bath at 80±10 ºC for 30±3 min, and then remove the extraction head; 3) GC-MS analysis: Insert the extraction head into the GC injection port for GC-MS analysis to obtain chromatographic mass spectrometric data of the sample; Chromatographic conditions: Column temperature was programmed to maintain at 40 °C for 5 min, then increased to 230 °C at 5 °C / min and maintained for 10 min; injection port temperature was 250 °C; carrier gas: high-purity helium; flow rate was 1.0 ml / min; split ratio was 5:1; Mass spectrometry conditions: electron bombardment ion source, ion source temperature 230 ºC; ionization energy 70 eV; full scan mode, scan range m / z 40-500; quadrupole temperature 150 ºC, connector temperature 240 ºC; 4) Data analysis: Import the chromatographic mass spectrometry data obtained in step 3) into the MassHunter software, search for compounds by chromatogram deconvolution or integral search, use the NIST database to identify compounds, and set the matching degree to 60%; calculate the content of the main compounds in the sample based on the retrieved compound peak area and internal standard peak area; and further calculate the relative content of 2-acetylpyrroline, hexanal, and 2-pentylfuran; 5) Aroma intensity evaluation: The aroma intensity score of popcorn aroma was calculated based on the relative contents of 2-acetylpyrroline, hexanal, and 2-pentylfuran; The relative content of hexanal and the relative content of 2-pentylfuran are both 9% as the dividing point; if the relative content of hexanal and the relative content of 2-pentylfuran are both less than 9%, the aroma intensity score is y=0.6751x1+7.3553; otherwise, the aroma intensity score is y=-0.05791x2-0.04181x3+8.4672; x1 is the relative content of 2-acetylpyrroline, x2 is the relative content of hexanal, and x3 is the relative content of 2-pentylfuran.

2. The method for evaluating the aroma intensity of popcorn aroma in rice according to claim 1, characterized in that: The standard adopted in step 1) is the National Standard of the People's Republic of China GB / T 15682-2008.

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